1. Field of the Invention
The invention relates to a volume measuring instrument or flow meter for measuring the flow of gaseous or liquid media and, in particular, to a flow meter having at least one rotatably movable measuring organ, a measured-value pickup device responsive to the measuring organ for obtaining an electrical quantity corresponding to the revolutions of the organ, and an evaluating device connected to the measured-value pickup device.
2. Background of the Invention
In one knwon flow meter of above type, the measured-value pickup device comprises a reed relay mechanism with a revolving support element driven by a rotatably movable measuring organ. This latter support element carries a mangetically conductive ring and is moved by the organ past the reed relay which is connected into a circuit with a supply voltage source and a counter. When the reed relay operates, both its contacts are closed and a current pulse flows to the counter. This known flow meter, therefore, requires the use of a separate supply voltage source, which may be formed, for example, by a storage battery.
Also known is another flow meter comprising an electronic pulse generator which contains a stationary coil. An a-c voltage is induced in this coil by a ring magnet coupled to and moved by a rotatably movable measuring organ included in the meter. This a-c voltage is processed in an evaluating device which contains, besides a voltage amplifier, a Schmitt trigger and an electronic counter. The aforesaid evaluating device requires for the operation of its individual parts a supply voltage, which is made available by a separate supply voltage source.
Thus, in all the known flow meters which employ a measuring organ and a measured-value pickup device responsive to the organ for deriving an electrical quantity corresponding to the revolutions of the organ, a separate supply voltage source is required. These meters thus differ in this respect from flow meters in which the processing of the picked-up measurement value and its evaluation are effected by number wheels driven by the movable measuring organ in a mechanical counting mechanism.
It is therefore an object of the present invention to provide a flow meter of the above type which does not require a separate supply voltage source.